Breaks up the soil, aerating the soil, relieving compaction and improving drainage.
Allows perennial weeds to be dug out and annual weeds to be dug in.
On heavier soils allows for good weathering, breaking up clods overwinter.
Good way to incorporate manure, compost and green manures into the soil.
Bring soil pests to the surface for hand picking or the birds.
Enables varying depth of cultivation.
But it is time consuming and needs skill to do it neatly and not leave a lot of levelling to be done later.